1. Field of Invention
The invention disclosed herein relates generally to a valve assembly for controlling flow of materials into a materials processing machine. More specifically, preferred embodiments of the disclosed invention relate to a valve assembly for controlling flow of granular material into a plastics processing machine, wherein the valve assembly is actuated via rotational motion of a valve.
2. Description of the Related Art
Existing granular material flow control valves generally are horizontally actuated and are commonly called slide shut-off valves. Slide shut-off valves depend on gravity to convey granular material and are commonly comprised of a rectangular metal slide plate with a circular or rectangular hole located asymmetric to the lateral centerline of the rectangular slide plate. The plate of a slide shut-off valve is mechanically contained between two stationary metal plates, to allow linear motion of the slide plate from a closed position to a fully open position. The center of a hole in the slide plate aligns with the center of the material source device, such a hopper or any point in between.
The slide shut-off device by its nature is prone to fouling caused by the dust contained within the granular material, thus rendering over time an inoperable valve requiring frequent maintenance and/or component replacement. The slide shut-off valve does not allow for fast material changes or self-purging. The slide shut-off valve is associated with undue material bridging and requires significant house-keeping. High maintenance costs are associated with the slide shut-off valve, which is also prone to invasion by moisture.
The slide shut-off valve is bulky and cumbersome to transport and usually remains located with the material processing equipment. In particular, the slide shut-off valve is not readily portable; material tends to bridge in a slide-shut off valve. The slide shut-off valve exhibits poor housekeeping because the very action of the slide plate, between the extremes of motion forces minute dust particles of the material to enter the atmosphere and larger particles to fall to the floor or other horizontal surface. A slide shut-off valve cannot effectively seal hygroscopic materials from atmospheric moisture.